Process for manufacturing highly oriented amorphous polyester filament yarns

ABSTRACT

In a process for manufacturing fast-spin highly oriented amorphous polyester filament yarns, the shock cooling is achieved by means of a rotating cooling surface formed by the contact surface of a cooling cylinder. Filament yarns having a desired boiling shrinkage up to 70% and a birefringence larger than 0.08 can be obtained by varying the duration of contact between the filament yarns and the cooling cylinder and/or the distance between the spinneret and the cooling cylinder.

This application is a continuation of application Ser. No. 07/432,742,filed Oct. 23, 1989, now abandoned.

FIELD OF THE INVENTION

The invention concerns a method for the production of highly orientedamorphous polyester filament yarns by means of melt spinning withwinding speeds of >4000 m/min, as well as an apparatus for theimplementation of the method.

BACKGROUND OF THE INVENTION

The production of a fast spun polyester filament yarn consisting of atleast 85 weight % of ethyleneterephthalate units, leads to a feeder-yarnwhich, because of its highly oriented amorphous qualities, is eminentlysuitable for false twist texturing. However, these properties can onlybe obtained if fast cooling can be effected at high winding up speeds.

Basically, two different methods were proposed to obtain such a shockcooling process.

Thus EP-A-O 089 819 describes a shock cooling process by means of water.In this process, a polyethyleneterephthalate filament yarn is cooled ina water bath at a rate of at least 5000 m/min. While being highlyoriented, the resultant yarn only has a low crystallinity, substantiatedby a boiling shrinkage of at least 45% and at most 68.5%.

However, cooling in water has serious drawbacks. First of all, the yarnis subjected to breaking in the water bath, resulting in high stresses.There occur problems with spraying water and the application of aspinning preparation onto the wet yarn. When using water cooling, thereoccurs a rapid increase in the water carried along adhering to thesurface, and hence in the spraying water, as the number of filamentsincreases.

As compared with shock cooling with water, an improvement has beenobtained with air cooling. Thus EP-A-O 244 216 describes a polyesterfilament yarn which is spun at a rate of over 5000 m/min in a highpressure chamber where a narrow tube is arranged at its outlet, shockcooling being obtained because of the Venturi effect. In the case of aircooling, the uniform cooling of the gathered filament bundle in thecooling tube (Venturi) is no longer ensured as the number of filamentsincreases.

Apart from the drawback of the high specific air consumption of up toapproximately 70 Nm³ /kg of polyethyleneterephthalate, it is notpossible to ensure a defined yarn speed in the range below thespinneret, exactly at the point where the most intensive cooling must beeffected.

Objects of the Invention

It is the object of the invention to provide a method for the shockcooling of a fast spun polyethyleneterephthalate filament yarn, whichensures a defined yarn speed in the cooling range.

A further object is to make available an apparatus for implementing theabove mentioned method.

Another object is to make available a polyester filament yarn with ahigh birefringence and a relatively high boiling shrinkage as a feederyarn.

Other objects and advantages of the invention will become apparent asthe description thereof proceeds.

DESCRIPTION OF THE INVENTION

The solution of the problem lies in a method which, is characterized inthat the melt spun filament yarns are cooled by means of a rotatingcontact surface, and that they are subsequently provided with a spinningpreparation and wound up.

A rotating contact surface has the advantage that an operation becomespossible under more defined conditions without a liquid or gaseousmedium. Irrespectively thereof, it is possible to determine the coolingrate by determining the distance of the cooling surface from thespinneret and the angle of contact of the yarn on the cooling surface.

Merely by varying the two parameters, it is possible to obtain a greatnumber of yarn properties.

It has proved to be expedient to choose the contact times of thefilament yarn on the contact surface between 1×10⁻³ and 1×10⁻² s, inparticular 2×10⁻³ -6×10⁻³ s, set with a range of the peripheral speed ofthe contact surface between 1600 to 2400 m/min. It is, of course, alsopossible to calculate the contact length or the angle of contact of thefilament yarn from the specification of the time.

The polyester yarn produced in accordance with the method, surprisinglyhas an undeformed circular cross section without coalescences. Thebirefringence values lie, depending on the setting, between 0.08 and0.11 and at the same time, a boiling shrinkage of >40% in particularbetween 40-70%, preferably at 45-60% with reference to the non-shrunkfilament yarn.

A rotating contact surface used as the cooling surface has provedsuitable as the apparatus for implementing the method.

A rotating contact surface has the advantage that it is possible to coola greater number of single filaments than was possible in the knownshock cooling processes. Thus it is readily possible to cool 30 and morefilaments simultaneously. The desired properties of the high shrinkageyarn (40-70% BS) can be obtained in a particularly simple way by varyingthe distance from the spinneret, as well as the circulating speed of thecontact surface.

According to a preferred mode of embodiment, the contact surface isdesigned as cooling roller. The cooling roller is preferably a hollowbody made of a material with good thermal conductivity and can beprovided with additional connections for a heat transfer medium or acooling medium. Such a roller ensures a freely selectable heat removalfor the polyester filament yarns.

A cooling belt is also suitable for the shock cooling of polyesterfilament yarns, the thickness of which depends on the flexibility of thebelt.

The contact surface expediently consists of a material with a goodthermal conductivity, preferably a metal or alloy. Copper, aluminum andtheir alloys are particularly suitable.

The thickness of the metal layer amounts to 2-100 mm, preferably 10-80mm, in particular 40-60 mm. The distance of the cooling roller from thespinneret amounts to 250-1000 mm, depending on the filament titre andoverall titre.

The invention will be described in greater detail with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in:

FIG. 1, a schematic representation of the method in accordance with theinvention with a cooling roller;

FIG. 2, a view according to FIG. 1 rotated by 90°;

FIG. 3, a schematic representation of a cooling belt.

According to FIG. 1, a spinneret is designated by 1. From the spinneret,there emerges a bundle of polyester yarn filaments 2, whose outerfilaments are designated by 2' and 2" respectively. Provision is madefor a cooling roller 3 between a guide roller 4 and the spinneret 1. Aresultant combined yarn 5 runs over a convergence point 6 where aspinning preparation is applied in the known way. Provision can be madefor an additional entangling device 7 ahead of a winding device 8.

In FIG. 2, the arrangement of FIG. 1 is shown rotated by 90°. Apart fromthe components of the apparatus of FIG. 1, there are indicated theconnections 11 for a heat transfer medium. The purpose of therepresentation is to illustrate the progress of the single filaments asfar as the convergence point 6. The number of the yarn filaments 2 islargely non-critical.

FIG. 3 shows a cooling belt 10 which is carried over rollers 9, 9' and9", at least one of these rollers being driven by means of a motor, notshown. The yarn filament bundle 2 arrives at the cooling belt 10 in theregion of the roller 9 and leaves the cooling belt 10 in the region ofthe roller 9' as the combined yarn 5, towards the winding device 8, notshown.

In operation, a polyester yarn filament bundle 2 emerging from thespinneret 1 arrives on the surface of the cooling roller 3 where itexperiences shock cooling during its contact with the roller surface. Inthis process, the cooling roller 3 is revolving at a peripheral speed of1600 to 2400 m/min. The yarn is fed to the winding device 8 via theguide roller 4 and via the convergence point 6 with a winding up speedof at least 4000 m/min. A possible stretching is determined by thedifference between the winding up speed and that of the cooling roller3.

If required, the action of the cooling roller can be enhanced by heatremoval by means of a cooling medium.

EXAMPLES OF APPLICATIONS Test Parameters

A standard polyester polymer with an intrinsic viscosity of 0.75 dl/gwas spun without godet rollers at a constant winding up speed of 5000m/min to the two titres dtex 67 f 12 and 200 f 30 (nom. 55 dtex f 12 and167 f 30).

The following parameters were varied:

    ______________________________________                                        the spinneret/roller distance                                                                        35-100    cm                                           the roller speed       1400-2400 m/min                                        the yarn contact length on the roller                                                                12-16     cm                                           ______________________________________                                    

Execution of the Tests

Instead of the crystallinity, the boiling shrinkage (BS) has beenindicated. The boiling shrinkage was determined by a length measurementbefore and after a heat treatment in water [BS measurement: a singlefilament, 50 cm in length (unshrunk): at 98° C.± 1° C. in water for 2.5minutes: mean value from 3 measurements]. With an approximately similarorientation of the yarns, the value of the boiling shrinkage may beconsidered as a comparative measurement of the crystallinitysubstantiated by density measurements of the filaments. By means of theresults of these measurements, the optimum spinneret cooling-rollerdistance was determined for the respective spinning titre and theproperties required for it. It is possible to influence the spinningresult by the spinneret cooling roller distance, the peripheral speed ofthe cooling roller and the filament cooling roller contact length (thiscorresponds to the cooling time). At a constant peripheral speed of thecooling roller and a constant contact length of the yarn on its surface,it is, above all, the boiling shrinkage that is affected by thespinneret cooling roller distance whilst the orientation does not showany clear cut tendency. The test results are represented in tables. FromTable 1, it may be gathered that with an increasing distance, the BS issubjected at first to a slight decline and when a limit is reached, inthe case described, approximately 55-60 cm, suddenly to a verypronounced decline.

                  TABLE 1                                                         ______________________________________                                        Peripheral cooling roller speed                                                                 2000 m/min                                                  Yarn contact length on the                                                                      16 cm = contact time: 4.8 ms                                cooling roller                                                                Spinning titre    67 f 12 dtex                                                Winding up speed  5000 m/min                                                  Dis-  30     35     40   45   50   55   60   65   70                          tance                                                                         spin-                                                                         neret                                                                         cooling                                                                       roller                                                                        [cm]                                                                          Boiling                                                                             66.3   67.0   67.0 71   68   66   62   19.6  4                          shrink-                                                                       age                                                                           [%]                                                                           Bire- 88.1   91.6   92.5 83.1 84   87.5 81.1 88.2 91.6                        fring-                                                                        ence ×                                                                  10.sup.3                                                                      ______________________________________                                    

By means of the variable angle of contact of the filament on the coolingroller periphery, it is possible to vary the contact time and hence thecooling time. By means of this parameter, the BS of the spun yarns isalso basically influenced. As the cooling time i.e. the contact length,is shortened, there appear, as shown in Table 2, the same trends in therelationships depending on the spinneret cooling roller distance, onlyat a lower level.

                  TABLE 2                                                         ______________________________________                                        Peripheral cooling roller speed                                                                 2000 m/min                                                  Yarn contact length on the                                                                      12 cm = contact time: 3.6 ms                                cooling roller                                                                Spinning titre    67 f 12 dtex                                                Winding up speed  5000 m/min                                                  Distance spinneret cooling                                                                   30     35     40   45   55   65                                roller [cm]                                                                   Boiling shrinkage [%]                                                                        58.0   56.6   54.0 56.6 49.0  8.3                              Birefringence × 10.sup.3                                                               87.9   77.6   88.1 81.1 97.0 90.2                              ______________________________________                                    

In contrast to the adjustment values of the cooling roller alreadyreferred to, where by altering them, it proved impossible to exert aclear cut influence on the orientation in a given direction, theorientation of the spun yarn can be set within certain limits by meansof the roller speed. As shown in Table 3, with an increasing speed theboiling shrinkage increases simultaneously, the increase below 2000m/min being pronounced and above this value being only slight, with acontrary trend in the orientation (birefringence).

                  TABLE 3                                                         ______________________________________                                        Spinneret cooling roller distance                                                               45 cm                                                       Contact length    12 cm = contact time: 3-4.5 ms                                                (depending on the cooling                                                     roller speed)                                               Spinning titre    67 f 12 dtex                                                Winding up speed  5000 m/min                                                  Roller speed [m/min]                                                                       1600    1800    2000  2200  2400                                 Boiling shrinkage [%]                                                                      21.0    32.0    56.6  62.0  66.0                                 Birefringence × 10.sup.3                                                             96.9    91.9    88.1  84.1  78.9                                 ______________________________________                                    

In spinning to the titre dtex 200 f 30 (nom. dtex 167 f 30) --a higherfilament titre and greater number of filaments--the spinneret coolingroller distance must be increased to approximately 80 cm because of theslowed down cooling ahead of the cooling roller in order to obtain aboiling shrinkage of >40%. Basically, however, the relationshipsascertained for the dtex 67 f 12 titre are preserved, as may be seenfrom the example of the cooling roller speed from Table 4.

                  TABLE 4                                                         ______________________________________                                        Cooling roller speed [m/min]                                                                   1600    1800    1900  2000                                   Boiling shrinkage [%]                                                                           32.0   44.0    53.0  57.0                                   Birefringence × 10.sup.3                                                                 103.5    102    99.5  96.0                                   ______________________________________                                    

A particular advantage of the method in accordance with the invention isseen in the fact that, in contrast to the known cooling processes withwater or air, the yarn properties can be specifically affected. Inaddition, the method in accordance with the invention operates moreeconomically, since it is neither necessary to make provision for an aircooling installation and its expensive operation, nor for preventivemeasures for incidental fouling by spraying water in wet operations.

    ______________________________________                                        DESIGNATIONS                                                                  ______________________________________                                         1         Spinneret                                                           2,2',2"   Filaments                                                           3         Cooling roller                                                      4         Guide roller                                                        5         Combined yarn                                                       6         Convergence point/spinning preparation                              7         Swirling                                                            8         Winding up device                                                   9,9',9"   Rollers                                                            10         Cooling band                                                       11         Pipe connection                                                    ______________________________________                                    

We claim:
 1. The method of producing a highly oriented amorphouspolyester filament feeder yarn for false twist texturing having aboiling shrinkage of 40 to 70%, which comprises melt-spinning apolyester in a spinneret into yarn filaments, shock-cooling themelt-spun yarn filaments by bringing them in contact with a cooledrotating surface at a distance of 35 to 60 cm from the spinneret for1×10⁻³ to 1×10⁻² seconds, and winding the yarn on a bobbin at a speed ofmore than 4500 m/min.